(a) Field of the Disclosure
The present disclosure relates to an automatic transmission for a vehicle. More particularly, the present disclosure relates to a planetary gear train of an automatic transmission for a vehicle that may improve power delivery performance and fuel consumption by achieving at least eleven forward speed stages using a minimum number of constituent elements, and may improve silent driving with little to no noise by using a driving point positioned at a low engine speed.
(b) Description of the Related Art
Recently, increasing oil prices have motivated vehicle manufactures all over the world to compete with respect to improving fuel efficiency. Particularly in the case of engines, manufacturers have been pursuing efforts to reduce the weight and improve fuel efficiency of vehicles by, for example, reducing engine size.
As a result, research into reduction of engine weight and enhancement of fuel efficiency through downsizing has been conducted. Further, research for simultaneously securing operability and fuel efficiency competitiveness through multiple speed stages has been conducted in the case of an automatic transmission.
However, in the automatic transmission, as the number of speed stages increases, the number of internal components also increases. As a result, the automatic transmission may be difficult to mount, the manufacturing cost and weight may be increased, and power transmission efficiency may be deteriorated.
Accordingly, development of a planetary gear train that may bring about maximum efficiency with a small number of components may be important in order to increase fuel efficiency through the multiple speed stages.
In this aspect, in recent years, 8-speed automatic transmission has been implemented. Also research and development of a planetary gear train capable of implementing more speed stages has been actively conducted.
A conventional automatic transmission of eight or more speed stages typically includes three or four planetary gear sets and five to seven engaging elements (frictional elements). Thus, mountability may be negatively affected due to an increase of volume and weight.
In this regard, disposing planetary gear sets in parallel or employing dog clutches instead of wet-type control elements is sometimes attempted. However, such an arrangement may not be widely applicable, and using the dog clutches may deteriorate shift-feel.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.